Doug has a good answer. To convince yourself take a photo of some very distant scene at some lower f, say 5.6. Then take some more photos by adjusting the lens using the distance scale and compare that to the theoretical hyperfocal distance. You will see how the smallest shift in distance will degrade your distant image before you reach the theoretical hyperfocal distance.

If you also have objects in your scene at a shorter distance try the same thing at f22. You may be surprized at how little is the degrading effect from diffraction compared to the improvement in depth of field.